Flying back from China through Hong Kong

My wife and I are flying to China for a few weeks in October on Air Canada,
she has a 10 year green card.
My question is in regards to flying back from Hong Kong, will she need anything as far as a visa to leave mainland China or will her green card and flight ticket be enough?
Looking online I did not find anything that was required except the green card and ticket but want to be sure we are correct.
Thanks.